tests/test-commit-copy.t

filectx: fix cmp() of file starting with '\1\n'

If file data starts with '\1\n', it will be escaped in the revlog to
create an empty metadata block, thus adding four bytes to the size in
the revlog size index. There's no way to detect that this has happened
in filelog.size() faster than decompressing each revision [1].

For filectx.cmp(), we have the size of the file in the working directory
available. If it differs by exactly four bytes, it may be this case, so
do a full comparison.

 [1]: http://markmail.org/message/5akdbmmqx7vq2fsg

  $ hg init dir
  $ cd dir
  $ echo bleh > bar
  $ hg add bar
  $ hg ci -m 'add bar'

  $ hg cp bar foo
  $ echo >> bar
  $ hg ci -m 'cp bar foo; change bar'

  $ hg debugrename foo
  foo renamed from bar:26d3ca0dfd18e44d796b564e38dd173c9668d3a9
  $ hg debugindex bar
     rev    offset  length   base linkrev nodeid       p1           p2
       0         0       6      0       0 26d3ca0dfd18 000000000000 000000000000
       1         6       7      1       1 d267bddd54f7 26d3ca0dfd18 000000000000